I'm using Bacula to backup to a disk file. The thing is, I'm backing up to an external USB disk and I want the backup to be robust to accidental unmounts of the external disk. Ideally, I would like to have the backup job stall if the disk isn't mounted (so it doesn't swamp the server's HDD) but resume when the disk is remounted.

I have accomplished the first objective by setting the backup directory to a specific directory on the external disk so that when the disk is unmounted, Bacula can't find it and the backup job gets stalled. When I remount the disk, however, the job fails to resume.